Intraluminally implantable frames may be implanted to treat a variety of conditions in a variety of fields. Frames implanted in vessels, ducts or channels of the human body can form part of a valve to regulate fluid flow within a body lumen or as scaffolding to maintain the patency of the vessel, duct or channel lumen. Implantable frames can also support a valve or valve leaflets for regulating fluid flow within a body lumen or for dilating a body lumen. One or more flexible valve leaflets can be attached to an implantable frame to form a medical device useful as an artificial valve. A variety of other implantable prostheses, such as stents, grafts and the like, also comprise an implantable frame placed within the body to improve the function of a body lumen.
The venous system includes a series of valves that function to assist the flow of blood returning to the heart. These natural valves are particularly important in the lower extremities to prevent blood from pooling in the lower legs and feet during situations, such as standing or sitting, when the weight of the column of blood in the vein can act to prevent positive blood flow toward the heart. This condition, commonly known as chronic venous insufficiency, is primarily found in individuals in which gradual dilation of the veins, thrombotic events, or other conditions prevent the leaflets of the native valves from closing properly. The failure of native valves to properly close can worsen, leading to significant leakage of retrograde flow such that the valve can become incompetent. Chronic venous insufficiency is a condition in which the symptoms can progress from painful edema to skin ulcerations. Elevation of the feet and compression stocking can relieve symptoms, but do not treat the underlying disease. Untreated, the disease can impact the ability of individuals to perform in the workplace or maintain their normal lifestyle.
One promising approach to treating venous valve insufficiency includes the implantation of self-expanding or radially-expandable artificial valves that can be placed using minimally invasive techniques. Recently, the development of artificial and biological valves has been employed to provide additional regulation of blood flow within blood vessels, such as veins. There are a variety of these valves described in the art, which are generally designed to allow normal flow of blood back to the heart, while preventing retrograde flow. However, dynamic fluctuations in the shape of the vein pose challenges to the design of implantable devices that conform to the interior shape of the vein. The shape of a lumen of a vein can undergo dramatic dynamic change as a result of varying blood flow velocities, pressures, and volumes therethrough. Implantable intraluminal prosthetic valves should be compliant enough to conform to the changing shape of the vein lumen and prevent irritation of the wall of the vein contacting the valve, but rigid enough to maintain vein patency and/or valve function within the vein. Blood flow within a vein is intermittent and bidirectional, subject to constant fluctuation in pressure and volume. These conditions may present challenges to designing an implantable frame suitable for placement inside the vein. An implantable frame lacking sufficient radial strength may collapse and/or fracture under the repeated fluctuations of vein diameter, while an implantable frame with undesirably high levels of radial strength may lack flexibility and may damage the vein by failing to compress in response to normal fluctuations in the vein diameter. Likewise, an implantable frame with a high surface area contacting the interior wall of a vein may induce inflammation or trauma in the vein wall, while an implantable frame with an insufficient surface area may lack sufficient durability.
What is needed is an intraluminally-placed medical device, such as a support frame, that provides structure for an artificial valve and is configured to distribute stress and strain forces within the frame during dynamic movement of a body vessel and intermittent fluid flow within the body vessel. In addition, medical devices are needed that provide sufficient radial strength to maintain vessel patency while being configured to prevent migration within the body vessel and minimize irritation of the body vessel. There also remains a need for a support frame configured with a radial strength to maintain patency of a body vessel while supporting a means for regulating fluid within the body vessel and minimizing irritation to the body vessel after implantation and/or extensive wear to the prosthetic valve leaflets during leaflet motion.